RO water is more convenient because you don't have to treat gallons of tap water from day to day. But, an RO filter needs installation and membrane changes periodically so the initial cost is higher. If you have human safe tap water and can easily treat it to remove the treatment chemicals (using Reptisafe) you can use it to spray your chams. If you have hard or sulphury unfiltered well water like I do the RO filter saves a lot of hassle and time. It was worth every penny.
I usually get the water in a new home tested to see just what's in it. For municipal water I ask the utility to give me a report. Then I can decide whether I want to put in an RO filter side faucet in the kitchen or not.
I'm using boiled tap water, left to cool in an open container. I do this because I feel the boiling will kill off any potential bugs and leaving it in an open container overnight allows the chlorine to evaporate. This is UK tap water so you will have to investigate your own local water. The breeder told me to just leave the water open overnight but I though boiling it can only be better.